GroupM is the world's largest advertising media company by billings. Headquartered in New York City, the company has over 36,000 employees and 400 offices in over 100 countries.

GroupM was formed in 2003 by WPP Group to serve as the parent company of WPP's media agencies, including Mindshare, MediaCom, [Wavemaker (media agency)|Wavemaker]], Essence Global, and m/SIX, as well as specialty businesses Xaxis, Finecast, Motion Content Group, and Kinetic. 

The company handles over 30% of the world's media billings, making it the world's largest media investment management operation. 

All of GroupM's agencies are independent global operations. GroupM works as a parent and collaborator in activities such as trading, content creation, digital advertising, finance, proprietary tool development and other business-critical capabilities. 

Through its agencies, GroupM offers advertising media selection services including: media planning and media buying, branded content, digital media, ROI and consumer research, internet marketing (digital, direct, search), content creation, social media marketing, out-of-home advertising and entertainment, sponsorship and sports marketing.

According to wikiwand